Slave system for a pair of hydraulic cylinders

ABSTRACT

A slave system for a pair of hydraulic cylinders and pistons for retracting one piston while the other piston is extended is provided with valves for venting excess hydraulic fluid when each piston reaches its fully retracted position. The line for the make-up fluid for the slave system is connected to a spool valve in the retracting or rearward end of each cylinder, and when each piston is fully retracted it forces a spool valve open to vent excess make-up fluid and slave fluid. The spool valve is springbiased to a closed position, and when the piston begins to extend the valve closes.

[ Dec. 11, 1973 United States Patent [191 Reinert I SLAVE SYSTEM FOR A PAIR OF Primary Examiner-Laurence M. Goodridge HYDRAULIC CYLINDERS [76] Inventor:

Assistant Examiner-Dennis Toth Gerald H. Remert, 6 Bnghtwood Rd Cold Spring y 41076 Attorney-Dawson, Tllton, Fallon & Lungmus Sept. 8, 1971 ABSTRACT [22] Filed:

Appl. No.: 178,762 A slave system for a pair of hydraulic cylinders and pistons for retracting one piston while the other piston is extended is provided with valves for venting excess g i l igg hydraulic fluid when each piston reaches its fully re- Field of 417/342 "acted The the make'up M the [52] US. [51] Int.

slave system is connected to a spool valve in the re- R f C1 d tracting or rearward end of each cylinder, and when a erences each piston is fully retracted it forces a spool valve UNITED STATES PATENTS open to vent excess make-up fluid and slave fluid. The spool valve is spring-biased to a closed position, and

3,494,290 2/l970 Schaible............... 417/342 FOREIGN PATENTS OR APPLICATIONS when the piston begins to extend the valve closes.

858,265 l/l96l Great Britain...................... 417/342 3 Claims, 3 Drawing; Figures SLAVE SYS'IEM 'F OR A PAIR OF HYDRAULIC .C YLINDERS BACKGROUND This invention relates to a slave system for a pair of hydraulic .cylinders, and the invention finds particular utility with concrete pumping machines.

Concrete pumping machines commonly use a pair of pumping cylinders for pumping the concrete and a pair of hydraulic cylinders for driving the pistons in the pumping cylinders. Each hydraulic cylinder includes a piston which is extended and retracted during the pumping cycle bp hydraulic fluid, and the piston in the hydraulic cylinderdrives the piston in the pumping cylinder by means of a rigid connecting rod or the like.

The hydraulic cylinders are conventionally synchronized for tandem operation so that one piston is being retracted while the other piston is being extended. This synchronization can be achieved by a slave system which includes a crossover pipe'connecting the forward ends of thehydraulic cylinders. As one of the pistons is being extended toward the forward end of the cylinder by hydraulic pressure, hydraulic fluid between the rod end of the piston and. the forward end of the cylinder, i.e., slave fluid, is forced through the crossover pipe into the otherihydraulic cylinder to force the second piston rearwardly. Conversely, when the hydraulic pump is switched to pump fluid into the other cylinder to extend the second piston, thesecond piston forces the slave fluid through the crossover to retract the first piston.

If there is any leak or dissipation of the slave fluid, there might not be sufficient slave fluid to fully retract the rearwardly moving 1 piston before the forwardly moving piston reaches its fully extended position. For this reason, concrete pumping machines have been provided with means for supplying make-up or auxiliary fluid 'to thecylin'ders between the forward ends of the cylinders and the rod ends of the pistons in order toensure that there will alwaysbe sufficient slave fluid to cause full retraction of the pistons. Since additional slave fluid is being added to the cylinders, some means should be providedfor venting this extra fluidwhen the retracting pistonreaches its fully retracted position. If the excess fluid is not vented, then the extending piston would not be able :to reach its fully extended position. Various means forventing the make-up'fluid are shown in US. Pat. Nos- :3,502,002, 3,279,282 (Re.26,820), and 2,998,781.

ltis'desirable that the venting means reliably vent the excess fluid during each stroke of each piston to preventthe occurrenceofa short stroke or a possibly dangerous pressure rise in the hydraulic system. It is also desirable that the venting means be both durable and easy to repair orreplace if necessary.

SUMMARY The invention provides venting means for a slave system which includes a valve-which is opened by direct mechanical actuation by the retracting piston. The valve will thereforenot.prematurely vent the make-up fluid, anddirect contact between the piston and the valve will open the valve prior to excessive pressure build-upsothat the extending piston will be allowed to complete its full stroke. Thevalve opens and closes by a shearing actiomandis pressure balanced so that the valve will operate independent of the ambient pressure.

The valve has a minimum of moving parts, and these parts can be easily replaced if necessary.

DESCRIPTION OF THE DRAWING The invention will be explained in conjunction with an illustrative embodiment shown in the accompanying drawing, in which:

FIG. 1 is a diagrammatic view of a pair of hydraulic piston and cylinder assemblies suitable for use in a concrete pumping machine which are provided with a slave system formed in accordance with the invention;

FIG. 2 is an enlarged fragmentary view of .a portion of FIG. 1; and

FIG. 3 is a fragmentary sectional view as would be seen along the line 3-3 of FIG. 2 without the internal parts of the valve. I

DESCRIPTION OF SPECIFIC EMBODIMENT 7 Referring to the drawing, the numeral 10 designates generally a driving assembly for operating a pair of pumping cylinders (not shown) in tandem. The driving assembly has particular utility in driving a pair of concrete pumping pistons such as described in my application entitled Concrete Pumping Machine, Ser. No. 66,744, filed Aug. 25, 1970, now US. Pat. No. 3,650,641.

The driving assembly 10 includes a pair of hydraulic cylinders 11 and 12 which slidably receive pistons 13 and 14, respectively. The rearward ends of the cylinders l1 and 12 are closed by end caps 15 and 16, and the forward ends are closed by end caps 17 and 18. A connecting rod 19 is connected to the piston 13 and extends slidably through the forward end cap 17 for connection to one of the pumping pistons. Similarly, connecting rod 20 extends slidably through the end cap 18 between the piston 14 and the other pumping piston.

Each of the pistons 13 and 14 can be driven to the forward or extended position occupied by the piston 13 by pressurized hydraulic fluid introduced into the cylinders 11 and 12 by the fluid supply conduits 21 and 22, respectively. The conduit 21 is connected to an internal fluid passage 23 in the end cap 15 which opens into the cylinder 11, and the conduit 22 is connected to an internal fluid pasage 24 in the end cap 16 which opens into the cylinder 12. The pressurized hydraulic fluid can be supplied by a conventional hydraulic pump p and conventional valving means V can be utilized to switch the pressurized fluid between conduits 21 and 22 to alternately drive the pistons 13 and 14.

In order to synchronize the movements of the two pistons so that one piston is retracted while the other is extended, a crossover pipe '25 is provided between the forward end caps17 and 18, and the cylinders are filled with hydraulic fluid forwardly of the rod ends of the pistons, i.e., the ends of the pistons to which the connecting rods 19 and 20 are secured. Accordingly, as the piston 13 is extended, the slave hydraulic fluid forwardly of the rod end of the piston is forced through the crossover pipe 25 into the forward end of the cylinder 12. Since the fluid supplyconduit 22 is vented to.

the fluid reservoir by the control valves when pressurized fluid is pumped through the conduit 21 the slave fluid which is forced through the crossover pipe forces the piston 14 rearwardly. The hydraulic fluid behind the head end of the piston 14, i.e., the end of the piston opposite the connecting rod 2 0, is freely forced 3 through the conduit 22 to the reseivoir as the piston 14 retracts.

Auxiliary or make-up fluid is supplied to the slave system through conduit 26 which is connected to the crossover 25 so that there is always sufficient slave fluid to force the piston 14 to the fully retracted position. The make-up fluid supplied by the conduit 26 can be pumped by the same hydraulic pump which supplies pressurized fluid to the conduits 21 and 22, but a restrictor 27 is interposed in the conduit 26 to reduce the rate of flow through the conduit 26 compared to the flow rates through the conduits 21 and 22. For example, the restrictor 27 can be chosen to reduce the flow rate through the conduit 26 to about one gallon per minute. Accordingly, even though fluid is being added to the slave system as needed, this fluid will not prevent the extension of piston 13 under the influence of the hydraulic fluid being pumped through conduit 21. A check valve 28 is positioned in the line 26 to permit only one way flow of fluid and to prevent fluid from being pumped through the line 26 by the extending piston.

In order to make sure that the piston 13 will reach its fully extended position, a valve assembly 29 is mounted within the end cap 16 for the cylinder 12. The valve assembly includes a spool closure member 30 which is slidably received in an axially extending bore 31 drilled in the end cap. A side port 32 extends radially inwardly from the side of the end cap to the bore, and another port 34 opens into the bore 31 and communicates with the fluid reservoir.

The spool 30 is provided with a pair of cylindrical end or head portions 35 and 36 which sealingly engage the cylindrical wall of the bore 31 and a central radially reduced portion 37. The bore 31 terminates in a radially reduced portion 38 which provides an annular shoulder 39, and the head 36 of the spool is resiliently urged against the annular shoulder 39 by a coil spring 40 which is held within the bore by a filler plug 41 and an externally threaded plug 42 which is threadedly engaged with the end of the bore.An actuating stem 43 extends forwardly from the head 36 through the reduced portion 38 of the bore into the bore of the cylinder l2.

A similar valve assembly 45 is provided in the end cap 15 for the cylinder 11.

A fluid line or conduit 46 which is connected to the make-up fluid supply conduit 26 downstreamof the check valve 28 branches into two lines 47 and 48 adjacent the rear ends of the cylinders. The line 47 is connected to the port 32 of the valve 29, and the line 48 is connected to the corresponding port of the valve 45.

The port is normally closed from the bore 31 by the head 35 of the spring-biased spool to block the line 47, and the spool of the valve 45 normally blocks the line 48. Accordingly, as the piston 13 is being extended, the hydraulic fluid forced from the cylinder 11 through the crossover pipe 25 together with the make-up fluid supplied through the conduit 26 force the piston 14 rearwardly toward the end cap 16. If the piston 13 should reach the fully extended position before the piston 14 reaches the fully retracted position, the make-up fluid will continue to force the piston 14 rearwardly even though movement of the piston 13 has stopped. On the other hand, if the piston 14 approaches the end of its return stroke before the piston 13 reaches the end of its forward stroke, the piston 14 will engage the actuator 43 andmove the spool rearwardly against the bias of the spring 40. As the head 35 of the spool moves rearwardly, the port 32 is allowed to communicate with the bore 31, and the make-up fluidand the fluid being forced from the cylinder 11 by the piston 13 is allowed to flow through the lines 46 and 47, through the port 32, bore 31 and port 34, and into the fluid reservoir R.

The spool will be maintained in the open position by the piston 14 until the piston 14 begins its return stroke under the influence of hydraulic fluid supplied through the conduit 22, and as the piston 14 moves forwardly, the spring 40 will urge the spool to the normal closed position in which the head 35 blocks the port 32.

The valve assembly 45 similarly includes a springurged spool which is movable to the valve-open 'position as the piston 13 reaches the end of its return stroke. The spring normally maintains the valve in the closed position in which the line 48 is blocked from the fluid reservoir R, but when the piston 13 moves the spool, the line 48 communicates with the reservoir to vent any excess make-up fluid and fluid being pumped by the piston 14 during its forward stroke.

The spool in each of the valve assemblies is pressurebalanced or equalized so that the spool will move to the valve-open position only under the influence of the pis- I ton. A passage or bore 51 is drilled through the end cap 16 to the passage 24 for the supply conduit 22 and communicates with the bore 31 through a port 52. The end of the passage 51 is closed by a threaded end plug 53. Since the passage 24 opens into the bore of the cylinder 12, the pressure of the fluid which acts on the forward end of the spool through the reduced portion 38 of the bore is the same as the pressure which acts on the rearward end of thespool through the passage 51 and port 52. Accordingly, the spool is not prematurely forced into the open position by hydraulic fluid pressure but will move rearwardly only under the influence of the piston.

The valve assembly has a minimum of moving parts,

and the port 32 which vents the excess make-up fluid is opened and closed by a simple shearing action of the spool under direct mechanical actuation by the piston. The valve assemblies are therefore quite'durable and reliable. Further, if either the spring orthe spool re quires replacing, these parts can be removed merely by removing the plug 42 and the filler'or spacer plug 41, and any necessary repair or replacement can be performed quickly in the field with a minimum of down time.

The end caps or cylinder closure members 15 and 16 can be formed from cylindrical blocks which are threadedly engaged with the ends of the cylinders, and the various ports and bores can be provided therein simply by drilling.

While in the foregoing specification a detailed description of a specific embodiment of the invention was set forth for the purpose of illustration, it is to be understood that many of the details herein given may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. In a hydraulically actuated pumping apparatus having a pair of hydraulic cylinders, each of the cylinders having an elongated bore, a retractable and extendible piston within the bore of each cylinder, hydraulic fluid supply means connected to each cylinder at one end thereof, valve means for the hydraulic fluid supply means for alternately supplying hydraulic fluid to each cylinder for alternately extending each piston, hydraulic fluid connecting means connected to each of the other ends of the cylinders for permitting hydraulic fluid to flow from one cylinder as the piston therein is extended to the other cylinder for retracting the piston in the other cylinder, and auxiliary hydraulic fluid supply means connected to each of the other ends of the cylinders for supplying auxiliary fluid to the cylinder in which the piston is retracting, the improvement characterized by a valve mounted on each cylinder at said one end thereof, each valve having a bore extending generally parallel to the axis of the associated cylinder and a pair of ports in the valve bore, a valve closure member slidable axially within the valve bore between a first position in which it blocks fluid flow between the ports and a second position in which fluid may flow between the ports, the auxiliary fluid supply means being connected to one of the ports of each of the valves, the valve closure member of each valve being movable by the piston in the associatedcylinder as the piston is retracted whereby the valve closure member is moved from the first to the second position and auxiliary fluid may flow from one of the valve ports to the other, each valve having a pressure-equalizing port in the valve bore communicating with the associated cylinder bore whereby the hydraulic pressure on opposite ends of the valve closure member is equalized.

2. The apparatus of claim 1 in which the valve closure member of each valve includes a spool slidable axially within the valve bore and having a radially enlarged head sealingly engaging the wall of the valve bore, and spring means within each valve bore for resiliently urging the spool toward the piston and into the first position in which the head of the spool closes said one port, the head of the spool being spaced from said one port when the spool is in the second position.

3. In a hydraulically actuated pumping apparatus having a pair of hydraulic cylinders, each of the cylinders having an elongated bore, a retractable and extendible piston within the bore of each cylinder, hydraulic fluid supply means connected to each cylinder atone end thereof, valve means for the hydraulic fluid supply means for alternately supplying hydraulic fluid to each cylinder for alternately extending each piston, hydraulic fluid connecting means connected to each of the other ends of the cylinders for permitting hydraulic fluid to flow from one cylinder as the piston therein is extended to the other cylinder for retracting the piston in the other cylinder, and auxiliary hydraulic fluid supply means connected to each of the other ends of the cylinders for supplying auxiliary fluid to the cylinder in which the piston is retracting, the improvement characterized by a valve mounted on each cylinder at said one end thereof, each cylinder including an end cap for closing the cylinder bore at said oneend of the cylinder, the valve for each cylinder being provided by a bore extending axially within the end cap thereof, each valve having a pair of ports in the valve bore at axially spaced locations, a spool slidable axially within the valve bore between first and second position, the spool having a radially enlarged head sealingly engaging the wall of the valve bore, the enlarged head being positioned to prevent fluid flow between the ports when the spool is in the first position and being positioned to permit fluid flow between the ports when the spool is in the second position, the auxiliary fluid supply means being connected to one of the ports of each of the valves, spring means for each valve for resiliently urging the spool thereof toward the associated piston and into the first position, the spool of each valve being engageable by the associated piston as the piston is retracted whereby the spool is moved from the first to the second position and auxiliary fluid may flow between the valve ports, the hydraulic fluid supply means for each cylinder including a fluid passage extending through the end cap thereof and communicating with the bore of the cylinder, each end cap being provided with a pressureequalizing passage communicating the hydraulic fluid passage therein with the valve bore whereby the hydraulic pressure on opposite ends of the spool head is equalized. 

1. In a hydraulically actuated pumping apparatus having a pair of hydraulic cylinders, each of the cylinders having an elongated bore, a retractable and extendible piston within the bore of each cylinder, hydraulic fluid supply means connected to each cylinder at one end thereof, valve means for the hydraulic fluid supply means for alternately supplying hydraulic fluid to each cylinder for alternately extending each piston, hydraulic fluid connecting means connected to each of the other ends of the cylinders for permitting hydraulic fluid to flow from one cylinder as the piston therein is extended to the other cylinder for retracting the piston in the other cylinder, and auxiliary hydraulic fluid supply means connected to each of the other ends of the cylinders for supplying auxiliary fluid to the cylinder in which the piston is retracting, the improvement characterized by a valve mounted on each cylinder at said one end thereof, each valve having a bore extending generally parallel to the axis of the associated cylinder and a pair of ports in the valve bore, a valve closure member slidable axially within the valve bore between a first position in which it blocks fluid flow between the ports and a second position in which fluid may flow between the ports, the auxiliary fluid supply means being connected to one of the ports of each of the valves, the valve closure member of each valve being movable by the piston in the associated cylinder as the piston is retracted whereby the valve closure member is moved from the first to the second position and auxiliary fluid may flow from one of the valve ports to the other, each valve having a pressure-equalizing port in the valve bore communicating with the associated cylinder bore whereby the hydraulic pressure on opposite ends of the valve closure member is eqUalized.
 2. The apparatus of claim 1 in which the valve closure member of each valve includes a spool slidable axially within the valve bore and having a radially enlarged head sealingly engaging the wall of the valve bore, and spring means within each valve bore for resiliently urging the spool toward the piston and into the first position in which the head of the spool closes said one port, the head of the spool being spaced from said one port when the spool is in the second position.
 3. In a hydraulically actuated pumping apparatus having a pair of hydraulic cylinders, each of the cylinders having an elongated bore, a retractable and extendible piston within the bore of each cylinder, hydraulic fluid supply means connected to each cylinder at one end thereof, valve means for the hydraulic fluid supply means for alternately supplying hydraulic fluid to each cylinder for alternately extending each piston, hydraulic fluid connecting means connected to each of the other ends of the cylinders for permitting hydraulic fluid to flow from one cylinder as the piston therein is extended to the other cylinder for retracting the piston in the other cylinder, and auxiliary hydraulic fluid supply means connected to each of the other ends of the cylinders for supplying auxiliary fluid to the cylinder in which the piston is retracting, the improvement characterized by a valve mounted on each cylinder at said one end thereof, each cylinder including an end cap for closing the cylinder bore at said one end of the cylinder, the valve for each cylinder being provided by a bore extending axially within the end cap thereof, each valve having a pair of ports in the valve bore at axially spaced locations, a spool slidable axially within the valve bore between first and second position, the spool having a radially enlarged head sealingly engaging the wall of the valve bore, the enlarged head being positioned to prevent fluid flow between the ports when the spool is in the first position and being positioned to permit fluid flow between the ports when the spool is in the second position, the auxiliary fluid supply means being connected to one of the ports of each of the valves, spring means for each valve for resiliently urging the spool thereof toward the associated piston and into the first position, the spool of each valve being engageable by the associated piston as the piston is retracted whereby the spool is moved from the first to the second position and auxiliary fluid may flow between the valve ports, the hydraulic fluid supply means for each cylinder including a fluid passage extending through the end cap thereof and communicating with the bore of the cylinder, each end cap being provided with a pressure-equalizing passage communicating the hydraulic fluid passage therein with the valve bore whereby the hydraulic pressure on opposite ends of the spool head is equalized. 